Master of Science in Civil Engineering (MSCE)


Civil and Environmental Engineering

Document Type



Because of the potential for serious train-vehicle accidents at or near railroad-highway grade crossings, preemption of traffic signals is a very important supplement to an active warning system. Preemption is the transfer of normal signal phasing to a special control mode with the purpose of clearing any vehicles that are queued within the dynamic envelope as the train approaches, and prohibiting signal phases that would allow additional vehicles in the track area while the train is present. The focus of this research was the determination of the Clear Track Green Interval (or the Queue Clearance Time). The clear track green interval is the most important component of the preemption process because this is the time allotted to clear any vehicles that are queued within the track dynamic envelope. The estimation of the amount of time needed for the Clear Track Green Interval is often left to the discretion of the traffic engineer. To date, the Louisiana Department of Transportation and Development has no explicit guidelines for the traffic engineers in their design of railroad preemption for traffic signals. This research describes the evaluation of three methodologies that can be used to acquire the clear track green interval for an intersection. The study provides a comparison of the calculated values versus the field (or observed) values with the objective being to show if the calculated times are adequate or if they provide too much time for the action thereby causing adverse affects to the intersection. The second objective of this research is to provide guidance to the traffic engineers in the design of railroad preemption for traffic signals. Based on the results and analysis of this research, the field observed method yielded a lower clear track green interval 71% of the time. Out of the remaining two methods, the Marshall/Berg method yielded lower results 29% of the time and the Northwestern method always yielded a longer time because of its conservative approach. The instances when the Marshall/Berg method yielded lower results has varying causes. The reasons included: intersections where the side approaches shared the phasing causing the track side approach to have to compete with the other approach to move beyond the track, red light runners causing the drivers to hesitate before proceeding out into the intersection, and geometry issues.



Document Availability at the Time of Submission

Release the entire work immediately for access worldwide.

Committee Chair

Chestor Wilmot